[填空题]
(a) A particular household usayih 0c7pj( -eehjk9n3.t 63bdha6/sx wy (ct5wl 4uixs a 1.8-kW heater $3.0 h/day$ (“on” time), four 100-W lightbulbs $6.0 h/day$, a 3.0-kW electric stove element for a total of $1.4 h/day$ and miscellaneous power amounting to $2.0 kWh/day$. If electricity costs $0.105 per kWh, what will be their monthly bill (30 d)? dollars per month
(b) How much coal (which produces $7000 kcal/kg$) must be burned by a 35%-efficient power plant to provide the yearly needs of this household? kg of coal
